Loading and transporting sensitive electronic equipment has presented numerous problems. Typically, such equipment is packed in a suitable shipping container. Even slight impacts or vibrations to the container, however, produce shock forces that may damage precision instruments if they are not properly supported within the container.
To adequately protect electronic equipment, it is well known to use heavy-duty containers molded from polyethylene for high impact strength. An example of this type of shipping container is disclosed in U.S. Pat. No. 4,284,202 issued Aug. 8, 1981 to Barstow Jr. It is also necessary to build into these rugged containers a shock-mitigation system that is capable of protecting the equipment from possible damage during shipping and other rough handling. One known system employs a mounting rack constructed from a plurality of welded vertical and horizontal frame members and shock mounts designed to hold the electronic equipment stationary and to absorb shocks.
The problem with that prior art electronic rack mounting frame is that the vertical and horizontal members are Gas Shielded Tungsten Arc (TIG) welded together to form an integral frame structure. Although the welded rack frame is sufficiently strong to withstand most impacts and transmit the forces produced thereby from the shock mounts to the electronic equipment without damage, there are difficulties associated with its construction.
First and foremost is the time required to weld the various frame members together and to correct any distortions caused during the welding process, which adds considerably to the cost of manufacturing the mounting rack. Because of imprecisions in the welding process, it is difficult to maintain alignment of the mounting holes which are used to secure the electronic equipment modules to the rack. A further disadvantage of a welded rack system is the storage space required to keep finished racks in stock in order to fill orders promptly.
A more recent prior art electronic rack mounting frame may be seen in U.S. Pat. No. 4,998,636. While the electronic rack mounting frame of this Patent is superior to those mentioned above, it has been found that its design requires numerous manufacturing steps and parts in order to properly fabricate the frame. One drawback which has been found is related to the use of threaded fasteners in the patented rack. The front and the rear of the rack are maintained in the desired rectangular shape by threaded fasteners creating a frictional force among parts by passing through a clearance hole in one part and into a threaded hole in another part. Tightening the screw urges the parts together. The problem (shape changing from a rectangle to a rhombus) is in large part due to the clearance hole which is larger in diameter than the fastener passed therethrough. Because of the difference in diametrical size, the only force holding the shape of the unit is the frictional force created by the clamping action of the threaded fastener; there is no structural resistance against movement. As one of skill in the art will readily recognize, moving the frame in shear against only the frictional force created by the clamping force of the fastener is orders of magnitude easier than moving the parts by shearing the fasteners. Creating a rombus from the intended rectangle is therefore relatively easy in the prior art.
Out of square racks are not favored by the purchasing industries and, therefore, are a drawback to the sales and the reputation of the producer. Remedying the condition is, therefore, desirable and important to the rack mounting frame art.